COMPARISON OF VASODILATORY EFFECT OF CARBON-DIOXIDE INHALATION AND INTRAVENOUS ACETAZOLAMIDE ON BRAIN VASCULATURE USING POSITRON EMISSION TOMOGRAPHY

Carbon dioxide (CO2) and acetazolamide are increasingly being used as vasodilators to detect cerebrovascular reserve capacity in patients of chronic cerebrovascular disease. The functional cerebrovascular reser ve or ability of cerebral Vessels to lower their resistance in respons e to decrease in cerebral perfusion pressure is expressed as change in cerebral blood flow from baseline under a vasodilatory stimuli. Theor etically a vasodilator causing maximum vasodilation, and thereby expre ssing complete reserve capacity would be more suitable for such a purp ose. We quantitatively compared the vasodilating effect of 5% CO2 inha lation and 1 g of intravenous acetazolamide by positron emission tomog raphy. Cerebrovascular reserve was quantified in six patients with chr onic cerebrovascular disease in is the same sitting using oxygen-15 la beled water ((H2O)-O-15) positron emission tomography at rest; during 5% CO2 inhalation and after 1 g intravenous acetazolamide. A significa nt linear correlation in both nonlesion hemisphere (r = 0.701, p < 0.0 01) and in lesion hemisphere (r = 0.626, p < 0.005) was found between CO2 and acetazolamide for cerebrovascular reserve capacity. This corre lation improved by considering cerebrovascular reserve per unit change in arterial carbon dioxide (r = 0.744, p < 0.001 in nonlesion hemisph ere and r = 0.721, p < 0.001 in lesion hemisphere). The quantitative v alue of global reserve capacity was different by CO2 stimuli (5.2%) an d acetazolamide (49.7%). Though a similar vasodilatory response is eli cited by both Vasodilators, acetazolamide seems to be more potent and therefore should be preferred to detect patients with exhausted cerebr ovascular reserve capacity.